1. Field of the Invention
The invention relates to single control proportioning valves for liquids, such as hot and cold water and, more particularly, to pinch tube valves, wherein a control cam is disposable between a pair of resilient valve tubes for engagement with each to control the degree of pinching of, and thereby the proportioning and flow rate through, the valve tubes.
2. Description of the Prior Art
The present invention is an improvement of the valve disclosed in U.S. Pat. No. 4,359,067. That valve includes a support structure defining an elongated valve cavity having a longitudinal axis and a pair of spaced resilient valve tubes disposed in the cavity and respectively providing communication between two fluid supply conduits and a fluid outlet. The valve tubes extend transversely of the cavity axis on either side thereof. A guide pin is fixed in the support structure and extends upwardly into the valve cavity from the bottom thereof coaxially therewith. An elongated, tapered cam member extends axially into the valve cavity between the valve tubes and has an axial bore therethrough for receiving therein the guide pin. The cam member has a cylindrical portion and an eccentric conical portion and is rotatably and axially slidably movable within the valve cavity. When the cam member is completely retracted within the valve cavity, its cylindrical portion engages the valve tubes and completely pinches them off. As the cam member is withdrawn or extended from the cavity, the conical portion thereof passes between the valve tubes, allowing them to expand and permitting an increasing flow rate therethrough, proportional to the amount of extension of the cam member. As the cam member is rotated, the eccentric conical portion presses or pinches the two valve tubes different amounts, so as to control the proportioning therebetween, all in a known manner.
In such prior valve constructions, the cam member must be lubricated, typically with a silicone lubricant. In use this lubricant is wiped onto the valve tubes, facilitating sliding movement of the cam member relative to the flexible valve tubes. This is particularly important in the case of new tubes, which are dry. Thus, if a new cam is inserted as a replacement part, along with replacement valve tubes, the cam must either be manually lubricated at the time of installation or, alternatively, must be pre-lubricated by the manufacturer. In the latter case, the lubrication can commonly be wiped off during storage, transportation and the like by the cam packaging, which may typically be a transparent plastic bag or similar container. Also, the cam may become damaged by handling.